1. Field of the Invention
This invention relates to an apparatus for evaluating an oxygen sensor. More particularly, it is directed to an oxygen sensor evaluation apparatus which includes a burner.
2. Description of the Prior Art
There are several known types of apparatus for the evaluation of an oxygen sensor. They include the following:
(1) An apparatus in which the oxygen sensor to be evaluated contacts the exhaust gas of an engine;
(2) An apparatus in which the oxygen sensor to be evaluated contacts a model gas, such as a mixture of H.sub.2, CO, HC, O.sub.2 and N.sub.2, for example, as disclosed in Japanese Patent Publication No. 42224/1986.
(3) An apparatus in which the oxygen sensor to be evaluated contacts the combustion gaseous product of a fuel, such as propane or butane, for example, as disclosed in SAE Paper 790143.
These three types of apparatus, however, have the following drawbacks, respectively:
(1) Although the apparatus which employs the exhaust gas of an engine is more accurate than the other two types, it is difficult to accurately establish the desired conditions for evaluation, such as an excess air ratio (fuel-air ratio) and temperature. It requires excessive time for evaluation and therefore it is expensive. (2) Although the use of a mixture of various kinds of pure gas makes it possible to establish an excess air ratio of high stability as compared with what can be achieved by the apparatus employing the exhaust gas of an engine or propane gas burner, a large amount of gas is required to attain a flow rate which is comparable to that of the exhaust gas of an internal combustion engine. It is difficult to accurately establish the temperature of the gas which is employed in a large quantity. The gas is expensive, as it is a mixture of various kinds of gases.
(3) This type of apparatus employs gas which is obtained as a combustion product when a mixture of combustible gas and air is burned by a burner, thus a gas heater is not required. Moreover, a large volume of gas can be obtained which makes it easy to achieve a high flow rate, therefore, it is used for a wide range of inspection purposes in various fields of industry. However, the combustion gas is a product of nearly perfect combustion and contains only a small amount of uncombusted matter, as opposed to the exhaust gas of the internal combustion engine of an automobile. Therefore, it is often the case that the characteristics of a sensor which are determined by the burner apparatus differ from those which are obtained when the sensor is actually used with an internal combustion engine.